1. Field of the Invention
The present invention relates to a laminated film having good transparency which is produced by a gravure coating method. In particular, the present invention relates to a laminated film having good transparency, gas barrier properties and moisture vapor barrier properties, and few flaws on a base film.
2. Description of the Prior Art
Packaging materials are required to have diverse functions. In particular, barrier properties against various gasses (gas barrier properties) for protecting contents in the package are important properties which have influences on preservation of food. The importance of the gas barrier properties is increasing because of diversification of distribution systems and packaging technology, the regulations on additives, and change of tastes.
Factors for deteriorating the quality of food include oxygen, light, heat, moisture and the like. Among them, oxygen is one of the main factors deteriorating the quality of food. Thus, barrier materials comprising metals or glass having gas barrier properties can cut off oxygen effectively and also they are indispensable materials for means for controlling the change of quality of food, for example, filling of inert gasses or vacuum packaging.
The barrier materials which have barrier functions against not only the oxygen gas but also various gasses, organic solvent vapors, aromas and the like are effective in preventing rusts, odors and sublimation, and widely used in various fields such as the food, cosmetic, agrochemical and pharmaceutical fields in the form of bags for sweets, packages for flakes of dried bonito, pouches for boil-in-the-bag foods, containers for carbonated drinks, and the like.
Among thermoplastic resin films, orientated films of polypropylene, polyesters, polyamides and the like are widely used as packaging materials since they have good mechanical properties, heat resistance and transparency. When these films are used as the packaging materials for food, the contained food may be denatured through oxidative degradation or by aerobic microorganisms, the flavor is lost because of the dissipation of aromas through the films, and the taste is deteriorated because the moisture in the atmosphere penetrates into the packaged food and then the food is wetted.
Also, films of transparent resin materials having high gas barrier properties such as polyvinyl alcohols, ethylene-vinyl alcohol copolymers and polyvinylidene chloride resins are available. However, the gas barrier properties of these resins as the packaging materials are still insufficient in comparison with the metals or glass materials which are used for canned or bottled foods.
As one of the methods for improving the gas barrier properties of such resin films, it is tried to laminate a layer comprising inorganic layered compound and resins on the resin films by applying a coating fluid containing the inorganic layered compounds and resins. However, the laminated films may not have sufficient transparency.